Film laminates have become an important article of commerce, finding a wide variety of applications including use within various articles; for example, as outer covers for personal care products such as diapers, training pants, incontinence garments, feminine hygiene products and the like. In addition, film laminates have found use in various other bodily articles such as garments, surgical gowns, protective workwear, wound dressings, bandages and the like. The films can provide the desired barrier properties to the article while other materials laminated thereto can provide additional desired characteristics such as abrasion resistance and/or good hand. In addition, in order to increase comfort of the wearer, film laminates are desirably “breathable” in the sense that the laminates act as a barrier to liquids but allow water vapor and air to pass therethrough. In addition, by achieving and maintaining high breathability it is possible to provide an article that is more comfortable to wear since the migration of water vapor through the fabric helps reduce and/or limit discomfort from excess moisture trapped against the skin. Thus, such an article can potentially contribute to an overall improved skin wellness.
While a variety of film laminates are known in the art, one particularly useful laminate uses a breathable barrier comprising a stretched filled microporous film. Such films are typically filled with particles or other matter and then crushed or stretched to form a fine pore network throughout the film. The pores result from the separation of the polymer from the filler particles. The film pore network allows gas and water vapor to pass through the film while acting as a barrier to liquids and particulate matter. The amount of filler within the film and the degree of stretching is controlled so as to create a network of micropores of a size and/or frequency to impart the desired level of breathability to the fabric. An exemplary stretched filled-film is described in commonly assigned WO Patent Application 95/16562 to McCormack which discloses a filled-film comprising a predominantly linear polyolefin polymer, a bonding agent and about 30 to 80% by weight calcium carbonate, wherein the filled-film can be stretched to impart breathability to the film. The stretched film may then be laminated to a nonwoven web to create a laminate that takes advantage of the strength and integrity of the nonwoven web and the barrier properties of the stretched film.
In addition to breathability of the film laminate, the ability of the garment to exhibit elastic properties allows the garment to provide better body conformance. However, providing a low cost laminate that achieves the desired conformance and breathability is problematic, particularly with stretched filled-films. In order to achieve good body conformance, the polymer composition of the film desirably has good stretch and recovery properties and yet must also be capable of allowing formation and retention of pores upon processing. Furthermore, the breathable film laminate must be sufficiently stable so as to maintain the desired characteristics while in use (e.g. at about 37° C. or body temperature) as well as over time and shelf-aging. For example, such garments will often be exposed to temperatures up to about 54° C. or more in transport, storage, or during additional processing. Often exposure to such temperatures can cause shrinkage of the film which results in buckling and/or puckering of the fabric. This results in a product that is less aesthetically pleasing and gives the impression of a product of lesser quality. Further, the buckling may result in delamination which, in addition to being aesthetically undesirable, can increase the risk that the film will be ripped or torn. Moreover, it has been found that these conditions can also decrease the breathability and reduce the stretch-recovery of the fabric.
Thus, there exists a need for a film and laminate thereof which is capable of providing good breathability (i.e. WVTR) and body conformance at body temperature. Further, there exists a need for such a film and laminates thereof that are sufficiently heat stable to maintain the desired properties when subjected to the conditions commonly experienced in further processing, storage and/or transportation. Further, there likewise exists a need for a low cost film and film laminate that provides good breathability and body conformance that has overall improved aesthetics and that does not suffer from shrinkage and/or excessive hysteresis.